The application claims the priority benefit of Japanese Patent Application No. 2003-198593 filed on Jul. 17, 2003.
1. Field of the Invention
The present invention relates to an improvement in an image scanning unit and an image forming apparatus for using it, which has a simple structure and an easy assembly and is capable of enhancing accuracy of image scanning.
2. Description of Related Art
Conventionally, it has been known an image scanning unit, which has an imaging lens system including lenses more than 1 group. In the conventional image scanning unit, an illuminating light source of a manuscript is moved in the sub scanning direction, and the reflected light from the manuscript is reduced and imaged on a lined photoelectric conversion element through the imaging lens system, and then a luminous flux imaged on the lined photoelectric conversion element is photo-electrically converted to be output as an image scanning signal.
In this image scanning unit, if the imaged luminous flux is deviated from the light receiving surface of the lined photoelectric conversion element in the optical axis direction, the scanning image is deteriorated. A distance between lenses is therefore adjusted in order for the scanning image to meet a drafting standard by adjusting a distance of each lens group in the image scanning unit.
Moreover, in the image scanning unit, the portion of a lens 2 contributing to the imaging of the lined photoelectric conversion element is the portion of area 3 which is surrounded by dotted lines, as shown in FIG. 1. The imaging performance such as aberration in the portion of the area 3 is scattered in the turning direction of the lens. Even thought the lens 2 is set such that the portion of the area 3 becomes parallel to the lined photoelectric conversion element 1, and the distance between the lens 2 and the lined photoelectric conversion element 1 is adjusted in order for the imaging position of the imaged luminous flux to be parallel to the lined photoelectric conversion element 1, if the portion of the area 4 is set to be parallel to the lined photoelectric conversion element 1, the imaging position of the imaged luminous flux may be deviated from the light receiving surface of the lined photoelectric conversion element 1 in the optical axis direction, and deterioration in an image quality is caused.
Especially for a lens used in an image scanning unit for scanning a color image, if an imaging position among a blue wavelength, a green wavelength, and a red wavelength is deviated in the turning direction of the lens, a color image is not well reproduced. Therefore, it is also necessary to adjust a lens in the turning direction.
In order to improve an image quality by adjusting the distance between lenses and the turning direction of lens, there has been known a conventional image scanning unit (For example, JPA-H11-337799). In such an image scanning unit, one lens barrel is divided into two lens barrels, and each lens is held by both of the divided lens barrels. Screw portions are formed in the circumference of one divided lens barrel and in the inner circumference of the other divided lens barrel, and then both of the screw portions are screwed together, and the distance between lens groups are adjusted by turning both of the divided lens barrels.
However, in this related art, if the distance between the lens groups held by each divided lens barrel is adjusted, each lens group is turned with the turning of the divided lens barrel. Therefore, there was a problem that the turning of the lens group and the adjustment of the distance are not separately carried out.
Moreover, in this related art, in order to prevent the winding down of the screw portions, a guide portion of turning direction is provided in the divided lens barrel. However, if the axis core of the guide portion and the optical axis center of the lens are decentered, the optical axis center is turned about the axis core of the guide portion with the turning of the divided lens barrel. An extremely accurate lens barrel should be manufactured in order to avoid such turning, but the manufacture of the extremely accurate lens barrel is difficult because the lens barrel shape is increasingly complicated.